In benchmarks I've seen CStore is about 50% slower than Parquet on Spark.

Where is the transactional requirement? This person is working with a copy of the real data.

ETLs only need to be written once and if he decided on a PSQL approach he'd be writing ETLs to send the data there too. He's probably going to find a number of consistency problems so trying to normalise all this data again will just result in more work that won't make his team of DS' more productive.

If he's at ~1 TB of data today, where will he be in a few years time? What's the point of putting infrastructure in place that won't last for the next 10+ years?